Cooling fin and manufacturing method of the cooling fin

ABSTRACT

A cooling fin includes fin parts integrally extending from a base part. Each fin part is partially formed at a slant so that a proximal end portion is straight and a distal end portion is wavy (corrugated). Each fin part is partially slanted to make each fin part wavier as coming closer to the distal end portion from the proximal end portion. In a manufacturing process of the cooling fin, firstly, a straight cooling fin is produced by extrusion molding (an extruding step). Subsequently, the distal end portion of each fin is partially bent in a direction intersecting an extruding direction into a wave shape (a bending step).

TECHNICAL FIELD

The present invention relates to a cooling fin for dissipating heat froma heat generating element such as a semiconductor device into a fluidand a manufacturing method of the cooling fin and, more particularly, toa cooling fin with high cooling performance and a manufacturing methodof the cooling fin.

BACKGROUND ART

Heretofore, a high-pressure-resistant and large-current power module tobe mounted in a hybrid electric vehicle, an electric vehicle, or thelike has to include a cooling structure having high heat dissipationperformance because of a large self-heating value of the semiconductordevice during operation. FIG. 19 shows one example of a power modulehaving a cooler. A module 90 comprises a semiconductor device 10 whichis a heating element, a heat spreader 20 supporting the semiconductordevice 10, and a cooler 130 joined to the heat spreader 20 andinternally provided with flow paths.

The cooler 130 internally includes a cooling fin 131 made of a materialhaving high heat conductivity (e.g. aluminum). The cooling fin 131 has aplurality of fin parts 131 a arranged in a row at equal intervals.Distal ends of the fin parts 131 a are connected with a cover plate 132.In the cooler 130, accordingly, flow paths 135 are formed between thefin parts 131 a to extend along the longitudinal direction of each finpart 131 a.

In such cooler 130, a boundary layer develops in coolant flowing througheach flow path 135 between the fin parts 131 a. This boundary layer is afactor which may deteriorate cooling performance. In order to break theboundary layer, therefore, there have been proposed an offset fin inwhich split small blocks constituting a cooling fin 131 are arranged ina staggered configuration, and a corrugated fin in which each fin partis of a wavy or corrugated configuration (for example,JP10(1998)-200278A).

However, the aforementioned conventional cooling fins have the followingdisadvantages. Specifically, in a manufacturing process of the offsetfin, as shown in FIG. 20, (A) a straight fin 91 is extruded by anextruder 50 through a die 51 formed with comb-teeth-shaped throughholes. Then, (B) small blocks 92 are produced from the fin 91 by cuttingand slit machining the fin 91. Finally, (C) the small blocks 92 arearranged in an offset pattern and blocked fin parts 93 are combined in astaggered configuration.

The above offset fin manufacturing process needs blocks in numbercorresponding to the desired number of offset positions. On the otherhand, to enhance the cooling performance of the offset fin, it isessentially necessary to increase the number of offset positions. Thisis likely to cause a cost increase for fin cutting, slit machining, andassembling, thus leading to a complicated manufacturing process and highcost thereof.

On the other hand, the corrugated fin is made in a sine or similar curveshape, which cannot be manufactured by extrusion molding. Accordingly,casting is generally utilized for manufacturing the corrugated fin.However, this casting cannot easily produce minute fins well as comparedwith the extrusion molding, thus making it difficult to increase thesurface area of each fin. A material available for the casting is poorin heat conductivity as compared with a material available for theextrusion molding. The cooling performance of the former material is notsufficient.

Both the offset fin and the corrugated fin are configured such that finparts uniformly extend from a base part. Accordingly, a coolant willflow at high speed in the vicinity of the center of each fin in a heightdirection thereof and at low speed in the vicinity of a proximal end ofeach fin joined to the base part. A heat exchange rate is thereforepoor. Furthermore, the distal end and its vicinity of each fin part farfrom the heating element has a small temperature difference from thecoolant as compared with the proximal end and its vicinity of each finpart close to the heating element. Thus, the heat exchange rate isfurther low.

The present invention has been made to solve the above problems whichmay be caused by the conventional cooling fins. The present inventiontherefore has a purpose to provide an inexpensive cooling fin withimproved cooling efficiency and a manufacturing method of the coolingfin.

DISCLOSURE OF THE INVENTION

Specifically, a first aspect of the present invention provides a coolingfin comprising a plurality of fin parts arranged in a row and a basepart integrally continuous to one ends of the fin parts to support thefin parts, wherein each fin part has a shape in which a proximal endportion continuous to the base part is straight and a distal end portionis wavy in a flow direction of a coolant which will flow through the finparts.

In the cooling fin of the invention, the fin parts are integrally formedeach extending from the base part and arranged in a row to flow pathstherebetween. Each fin part has the proximal end portion of a straightshape and the distal end portion partially slanted to provide a waveshape (corrugated shape) in the coolant flow direction (a direction froman entrance to an exit of the coolant). Specifically, each fin partcontinuously changes so that the cross section of each fin part in adirection perpendicular to the height direction on the distal end sideis wavier than the cross section of each fin part on the proximal endside. Resistance between each fin part and a fluid becomes greater as aportion of each fin is closer to the distal end, so that the fluid, i.e.coolant, is not allowed to flow smoothly each flow path.

In other words, the coolant is allowed to flow more smoothly througheach flow path as it is closer to the proximal end. Thus, a flow rate ofthe coolant in the vicinity of the proximal end will increase. That is,the coolant will flow in larger amount on the side closer to theproximal end which is a bottom in the height direction of each fin part.Accordingly, the cooling performance of each fin part near the proximalend is enhanced. A heat generating element is placed near the proximalends of the fin parts to efficiently dissipate heat. On the other hand,the distal end portion of each fin part is formed into a wave shape(corrugated shape). The fluid, i.e. coolant, will therefore collide withthe fin parts and hence becomes turbulent, thereby inducing breakage ofa boundary layer which tends to develop in the coolant flow. Thus, ahigh cooling performance can also be achieved even in the vicinity ofthe distal end. Because of the above two reasons, the coolingperformance of the entire cooling fin can be enhanced.

In the cooling fin of the invention, preferably, the distal end portionof each fin part has a wave shape designed to meet an expression (I):

a≧f−w  (I)

where “f” is a pitch of the fin parts, “w” is a thickness of each finpart, and “a” is a height of the wave shape of each fin part.

Specifically, when the above expression (I) is satisfied, an areaallowing the coolant to linearly flow is decreased in each flow path onthe distal end side. Accordingly, the coolant is caused to meander,thereby reliably reducing the thickness of the boundary layer. Thecooling performance can therefore be enhanced.

According to another aspect, the invention provides a manufacturingmethod of a cooling fin comprising a plurality of fin parts arranged ina row and a base part integrally continuous to one ends of the fin partsto support the fin parts, the method comprising the steps of: extrudinga straight shaped fin including a plurality of fin parts each extendingfrom the base part into a comb teeth shape; and partially bending adistal end portion of each straight fin part in a direction intersectingan extruding direction to shape the distal end portion into a wave shapein a flow direction of a coolant which will flow through between the finparts.

In the invention, in the extruding step, the straight shaped cooling finis produced by extrusion molding. Thus, the fin parts can be formed infiner shape as compared with a cooling fin produced by casting. Theextrusion molding allows the use of a high heat conductive material. Thecooling performance is therefore high. Furthermore, the manufacturingmethod is suitable for mass production to manufacture the cooling fin atlow cost.

In the bending step, the distal end portion of each fin part is bentinto a wave shape (corrugated shape). Specifically, unlike the offsetfin, a cooling fin can be formed singly in a wave shape without needinga plurality of split blocks. Accordingly, the invention can provide asimpler manufacturing process with less number of components and processsteps as compared with the offset fin. According to the cooling finproduced by the manufacturing method, a wave angle (a bending angle) anda wave pitch of the fin parts can be determined to adjust the coolingperformance.

Furthermore, in the present invention, the cooling fin with a straightproximal end portion and a wavy distal end portion is produced by thetwo steps, that is, the extrusion molding step and the bending step.Accordingly, the cooling fin with high cooling performance can bemanufactured in simple steps.

In the bending of the invention, preferably, the bending step includesarranging a jig in a clearance between the fin parts and bending the finparts with the jig by cold working. The bending technique in a coldcondition (at a room temperature) includes for example placing the jigon one side and the other side of each fin part in a staggered pattern,and applying a load on the fin part by at least the jig placed on oneside. This makes it possible to manufacture the fin parts with theproximal end portion having a straight shape and the distal end portionhaving a wave shape. In such cold bending in the cold working, existingfacilities are available.

The bending step of the invention, preferably, includes placing the jigin a position corresponding to clearances between the fin parts havingjust been extruded, and bending the fin parts with the jig by hotworking. In the bending technique in a hot condition, for example, thejig has comb teeth insertable in clearances (slits) between the finparts, and the bending step further comprises moving the jig in adirection intersecting the extruding direction. According to thismethod, the entire cooling fin is high in temperature because of justafter extrusion and hence the fin parts can be processed easily. Thus, aload on the jig is small in the bending work. Because the heat derivingfrom the extrusion working is utilized, it is unnecessary to increasethe temperature of each fin part in hot working. This makes it possibleto shorten a manufacturing time and make efficient use of energy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing a schematic configuration of apower module in a preferred embodiment;

FIG. 2 is a perspective view showing a schematic configuration of acooling fin in the embodiment;

FIG. 3 is a plan view showing the schematic configuration of the coolingfin of FIG. 2;

FIG. 4 is a partial enlarged view showing the details of a portion ofthe cooling fin enclosed by a circle X of a dashed line in FIG. 2;

FIG. 5 is a sectional view of the cooling fin taken along a line A-A inFIG. 3;

FIG. 6 is a sectional view of the cooling fin taken along a line B-B inFIG. 3;

FIG. 7 is a sectional view of the cooling fin taken along a line C-C inFIG. 3;

FIG. 8 is a schematic view showing a flow speed distribution in acooling fin in a conventional art;

FIG. 9 is a schematic view showing a flow speed distribution in thecooling fin in the embodiment;

FIG. 10 is a view showing a shape (a straight shape) of a fin afterextrusion molding;

FIG. 11 is a schematic view showing an outline of a fin bendingoperation by cold working;

FIG. 12 is a schematic view showing an outline of a fin bendingoperation by hot working (extrusion of a straight fin);

FIG. 13 is another schematic view showing the outline of the fin bendingoperation in hot working (bending of the straight fin);

FIG. 14 is a perspective view showing a schematic configuration of a jigused in the hot working;

FIG. 15 is a view showing each size of a wavy portion of the coolingfin;

FIG. 16 is a graph showing correlation between a wave pitch, a waveangle, and pressure loss in each cooling fin;

FIG. 17 is a graph showing correlation between a wave pitch, a waveangle, and a heat transfer rate in each cooling fin;

FIG. 18 is a perspective view showing a modified form of a cooler;

FIG. 19 is a perspective view showing a schematic configuration of apower module in a conventional art; and

FIG. 20 is a perspective view showing an outline of a manufacturingprocess of an offset fin.

BEST MODE FOR CARRYING OUT THE INVENTION

A detailed description of a preferred embodiment of the presentinvention will now be given referring to the accompanying drawings. Inthis embodiment, the invention is applied to a cooling fin to be builtin a cooler of a vehicle-mounted intelligent power module.

Configuration of Power Module

A power module 100 in this embodiment includes, as shown in FIG. 1, asemiconductor device 10 which is a heat generating element, a heatspreader 20 on which the semiconductor device 10 is placed, and a cooler30 internally provided with flow paths for coolant. In the power module100, heat from the semiconductor device 10 will be dissipated into thecooler 30 through the heat spreader 20.

The semiconductor device 10 is a device such as IGBT constituting aninverter circuit. It is to be noted that much more semiconductor devicesare installed on a vehicle-mounted power module but only a part thereofis schematically illustrated for facilitating explanation.

The heat spreader 20 is made of a high heat-conductive material todissipate heat from the semiconductor device 10. The heat spreader 20 isintegrally brazed to the cooler 30. A fixing method of the heat spreader20 to the cooler 30 is not limited to the brazing. As an alternative,the heat spreader 20 may be fixed to the cooler 30 with a bolt.

The cooler 30 includes a cooling fin 31 and a cover plate 32 joined to adistal end of the cooling fin 31. The cooling fin 31 is made of amaterial, such as aluminum alloy, having high heat conductivity andbeing light in weight. In the cooler 30, flow paths 35 for coolant aredefined by the cooling fin 31 and the cover plate 32. The coolant may beselected either liquid or gas. In this embodiment, cooling water issupplied as the coolant to the flow paths 35.

Configuration of Cooling Fin

The details of the cooling fin 31 are explained below. FIG. 2 is aperspective view of the cooling fin 31 and FIG. 3 is a plan view of thecooling fin 31.

The cooling fin 31 is constituted of fin parts 1 arranged in a row atequal intervals and a base part 2 integral with the fin parts 1 tosupport the fin parts 1. Each fin part 1 has such a shape that aproximal end continuous to the base part 2 is straight in a flowingdirection of the coolant (a direction from an entrance to an exit of thecoolant (i.e., from IN to OUT in FIG. 1)) and a distal end is wavier.

To be specific, each fin part 1 of the cooling fin 31 in this embodimentis constituted of first regions 11 vertical to the base part 2, secondregions 12 each slanting at a predetermined angle with respect to thebase part 2, and third regions 13 joining the first region 11 and thesecond region 12. A set of the first to third regions 11 to 13 is shownin FIG. 4 (an enlarged view of a portion enclosed by a circle X of adashed line in FIG. 2). The first region 11 is of a nearly trapezoidalshape having a lower side at the proximal end and an upper side at thedistal end so that the lower side is wider than the upper side. Thesecond region 12 is of a nearly rectangular shape. The third region 13is of a nearly triangular shape having a side corresponding to a ridgeline joining between the upper side of the first region 11 and the upperside of the second region 12.

In each fin part 1, the first region 11 and the second region 12 extendto form the fin part 1 from the same straight line of the base part 2.In other words, the shape of the fin part 1 is straight in the proximalend because the lower side of the first region 11 is continuous to thelower side of the second region 12. The first region 11 extendsvertically with respect to the base part 2 as shown in FIG. 5 (asectional view along a line A-A in FIG. 3). The second region 12 isslanted at the predetermined angle with respect to the base part 2 asshown in FIG. 6 (a sectional view along a line B-B in. FIG. 3).

On the other hand, at the distal end of each fin part 1, the upper sideof the first region 11 and the upper side of the second region 12 arecontinuous to each other via the third region 13, so that the shape ofthe distal end of each fin part 1 is wavy (corrugated) in the coolantflow direction. The third region 13 has a nearly triangular shape havingan apex located at the proximal end of the fin part 1 and a width beingwider as coming closer to the distal end. Specifically, a portionbetween the first region 11 and the second region 12 in FIG. 3 includesa proximal-end-side portion vertically extending upward as a part of thefirst region 11 and a distal-end-side portion slightly slanting as thethird region 13 as shown in FIG. 7 (along a line C-C in FIG. 3).

The cooling fin 31 in this embodiment is expected to greatly enhancecooling performance as compared with the conventional cooling fin on thefollowing two grounds. FIG. 8 shows a flow speed distribution in astraight fin of a conventional shape. In the conventional configuration,specifically, the flow speed of the coolant reaches a peak in an area onor around the center (within a centermost broken line in FIG. 8) of eachflow path in the height direction of each fin part 1 (a verticaldirection in FIG. 8) and is slow in an area on or around the proximalend. Accordingly, the cooling performance is poor in the vicinity of theproximal end of each fin part 1. The coolant flow speed is similarlyslow even in the vicinity of the distal end of each fin part 1. Thedistal end side is far from the semiconductor device 10 which is theheat generating element and therefore has a small temperature differencefrom the coolant. Thus, the cooling performance is also poor in thevicinity of the proximal end.

On the other hand, FIG. 9 shows a flow speed distribution in the coolingfin in the present embodiment, having a straight proximal end and a wavydistal end. In this embodiment, the cross-section of each fin part 1 inthe direction perpendicular to the height direction is shaped to bewavier on the side closer to the distal end than the proximal end.Accordingly, resistance between each fin part 1 and the coolant islarger on the distal end side than the proximal end side, thereby makingthe coolant hard to flow. Thus, a peak (within a centermost broken linein FIG. 9) of the coolant flow speed comes close to the proximal end ascompared with that in the straight fin, so that a flow amount of thecoolant increases in the vicinity of the proximal end (First grounds).This makes it possible to enhance the cooling performance in thevicinity of the proximal end of each fin part 1.

Each fin 1 is of a wave shape (corrugated shape) in the vicinity of thedistal end. When a coolant collides with such fin part 1, the flow ofcoolant is caused to become turbulent. It is therefore expected to breakthe boundary layer (Second grounds). Consequently, high coolingperformance can be obtained even in the vicinity of the proximal end.

Manufacturing Method of Cooling Fin

An explanation will be given below to the manufacturing method of thecooling fin 31. A manufacturing process of the cooling fin 31 includesan extruding step of producing a straight fin by extrusion molding and abending step of bending a part of each fin part into a wave shape.

In the manufacturing process of the cooling fin 31, firstly, a fin isproduced in the extruding step by extrusion molding which is inexpensiveand adequate for mass production. At that time, a fin 310 is molded as astraight fin having a plurality of fin parts 1 as shown in FIG. 10. Thisis because a final fin shape including a wavy distal end and a straightproximal end is so complicated as not to be produced by only extrusionmolding. The straight fin 310 is therefore first produced.

In the bending step, subsequently, the distal end portion of each finpart 1 is shaped to be wavy. In this bending step, as shown in FIG.11(A), for example, a special jig 6 is placed on both sides of each finpart 1. This jig 6 is constituted of supporting jigs 61 and 62 which aredisposed on one side of each fin part 1 and a loading jig 63 which isdisposed on the other side. The jigs 61 to 63 are arranged in astaggered pattern so that the supporting jig 61, the loading jig 63, andthe supporting jig 62 are positioned in the order from upstream in thecoolant flow direction along the fin part 1.

As shown in FIG. 11(B), thereafter, the loading jig 63 applies a load onthe fin part 1. The fin part 1 is thus plastic deformed partially in adirection intersecting the extruding direction into a wave shape asshown in FIG. 2. To be concrete, a slant surface contacting with theloading jig 63 forms the second region 12 of the fin part 1 and surfacescontacting with the supporting jigs 61 and 62 form the first regions 11of the fin part 1. Each surface located between the adjacent jigs formthe third region 13 of the fin part 1.

The bending step may be not only the above cold working (at roomtemperature) but also a hot working to be performed just after theextruding step. In this hot working, as with the cold working, theextruding step is executed to produce a straight fin by normal extrusionmolding. Specifically, as shown in FIG. 12, a die 51 for producing thestraight fin 310 is attached to a molding machine 50. A billet 52 isloaded in the molding machine 50 and a pressurizing member 53 pressesthe inside of the molding machine 50. Thus, the straight fin 310 havingthe straight fin parts 1 as shown in FIG. 10 is extruded out through thedie 51.

Just after the straight fin 310 is extruded, a special jig 7 is placedacross the fin parts 1 as shown in FIG. 13. The jig 7 has a comb shapehaving a plurality of comb teeth 71 as shown in FIG. 14. Each of thecomb teeth 71 of the jig 7 is inserted between the fin parts 1. In thisstate, in conformity to the wave shape of the cooling fin 31, the jig 7is periodically moved in a direction intersecting the extrudingdirection in plan view seen from above in the height direction of thefin parts 1. Accordingly, the fin parts 1 are deformed in a hotcondition into the wavy or corrugated shape as shown in FIG. 2.

In the above hot working, the temperature of the fin parts 1 is high(about)600° because of just after the extruding step. Accordingly, thefin parts 1 can be bent easily and thus the jig 7 receives only a smallload during working. The jig 7 therefore can have good durability.Because of just after the extruding step, furthermore, the heat derivingfrom the extruding step can be utilized. It is therefore unnecessary toincrease the temperature of the cooling fin 31 for the bending step.This makes it possible to shorten a manufacturing time and efficientlyutilize energy. On the other hand, the above cold working can be handledby existing facilities, leading to a low initial cost.

Material of Cooling Fin

A material to be used in the extrusion molding is one of aluminumalloys, especially, an aluminum alloy with high heat conductivity. Table1 shows comparison in heat conductivity between materials. In Table 1,the materials are expressed based on the Japanese Industrial Standards(JIS).

TABLE 1 Heat conductivity Technique Material [W/mK] Extrusion A6063 209(Present embodiment) Casting ADC12 92

Casting is one of the techniques for molding the cooling fin 31.However, a material (e.g. ADC12) to be used in the casting is also analuminum alloy but it has lower heat conductivity than the material(e.g. A6063) to be used in the extrusion molding. The cooling fin 31 inthis embodiment is made by the extrusion molding and therefore can havehigher cooling performance than that made by the casting.

Size of Cooling Fin

As mentioned above, the shape of the cooling fin 31 is likely to have alarge influence on the cooling performance and the moldability. It istherefore important to meet a predetermined size requirement. FIG. 15shows parameters of the wave shape (corrugated shape) of the cooling fin31 on the distal end side. Each parameter represents as follows.

θ: Bending angle of a wave shape (hereinafter, Wave angle)

P: Pitch of a wave shape (hereinafter, Wave pitch)

f: Pitch of fin parts (Fin pitch)

w: Fin width (thickness)

a: Fin bending amount

c: Length of a straight portion

The fin bending amount “a” is equivalent to a difference (height of thewave shape of each fin part 1) in position in a direction perpendicularto the reference surface between one surface (a reference surface) ofthe first region 11 and a surface of the second region 12 continuous tothe reference surface in the distal end of each fin part 1.

In the cold working for corrugating the fin parts 1 by the jig 6,normally, the supporting jigs 61 and 62 are equal in width to theloading jig 63. Accordingly, the following explanation is given assumingthat the length of a straight portion of each first region 11 of the finpart 1 is equal to the length of a straight portion of each secondregion 12.

The conditions the above parameters should satisfy are represented byexpressions (1) to (4). The wave pitch (P) can be represented by thefollowing expression (1) using the length (c) of the straight portion ofthe fin part 1, the bending amount (a) of the fin part 1, and the waveangle (θ):

P=2(c+a/tanθ)  (1)

As the wave angle (θ) in the expression (1) is larger, the turbulence ofcoolant flow is more induced, thereby enhancing the cooling performance.However, if the wave angle (θ) is too large, the fin part 1 is likely tobe broken in the bending step. Assuming a design angle regarded as abreaking limit is a, accordingly, the wave angle (θ) has to meet thefollowing expression (2):

θ≦α  (2)

The jig 6 (or the jig 7, hereinafter omitted) is placed in contact withthe straight portion over its length (c) in the bending step.

If the length (c) is desired to be short, therefore, the jig 6 to beinserted between the fin parts 1 must be narrow in width. Narrower thewidth of the jig 6, the strength of the jig 6 tends to be lower, whichis likely to cause breakage of the jig 6. Assuming a design lengthregarded as a breaking limit of the straight portion of the jig 6 is β,the length (c) of the straight portion has to meet the followingexpression (3):

c≧β  (3)

If the bending amount (a) of each fin part 1 is small, it is notexpected to break the boundary layer. In order to break the boundarylayer and enhance the cooling performance, it is preferable to cause thecoolant to meander through each flow path 35 by reducing an areaallowing the coolant to linearly flow in each flow path 35.Specifically, it is desired to meet the expression (4):

a≧f−w  (4)

The shape of the cooling fin 31 is determined to satisfy the desiredcooling performance by changing the wave pitch (P) and the wave angle(θ) in a range that meets the above expressions (1) to (4). In otherwords, the size is selected to achieve the cooling performance mosthighly in such a range as not to break the fin parts 1 and the bendingjig 6.

An explanation will be given to correlation of the wave pitch (P) andthe wave angle (θ) of the cooling fin 31 with the cooling performance.FIG. 16 shows correlation of P and θ with pressure loss. FIG. 17 showscorrelation of P and θ with heat transfer rate. In both the figures;concrete numerals are not indicated and the cooling performance(pressure loss and heat transfer rate) is expressed as 1 by assuming anarbitrary wave angle (θ) is 1. In FIGS. 16 and 17, a plot using whitecircles shows the cooling performance when the length (c) of thestraight portion is equal but the wave angle (θ) and the wave pitch (P)are different between the cooling fins 31. A plot using black circlesshows the cooling performance when the wave pitch (P) is equal but thewave angle (θ) and the length (c) are different between the cooling fins31.

It is found in both figures that, as the wave angle (θ) is larger andthe wave pitch (P) is narrower, the pressure loss or the heat transferrate increases. In other words, it is found that the cooling performancecan be adjusted by the wave angle (θ) and the wave pitch (P) of the bentfin part 1.

The cooling fin 31 in the present embodiment, as explained above indetail, each fin part 1 is partially formed at a slant so that theproximal end portion is straight and the distal end is wavy(corrugated). Such configuration allows the coolant to flow moresmoothly in the vicinity of the proximal end than in the vicinity of thedistal end, thereby increasing the flow rate of the coolant flowingalong the vicinity of the proximal end. This makes it possible toenhance the cooling performance in the vicinity of the proximal end ofeach fin part 1 located close to the semiconductor device 10. On theother hand, the distal end portion of each fin part 1 located far fromthe semiconductor device 10 is wavy. Thus, the coolant becomes turbulentwhen collides with the fin parts 1, inducing breakage of the boundarylayer. Accordingly, high cooling performance can also be obtained in thevicinity of the distal end of each fin part 1.

In the manufacturing process of the cooling fin 31 in the presentembodiment, firstly, the straight-shaped cooling fin 310 is produced byextrusion molding (the extruding step). The fin parts 1 can therefore beformed in smaller or finer shape as compared with the cooling finproduced by casting. Furthermore, a high heat conductive material can beused and hence high cooling performance can be achieved. The cooling fin310 is suitable for mass production and can be manufactured at low cost.

Successively, the distal end portion of each fin part 1 is partiallybent in the direction intersecting the extruding direction into a waveshape (the bending step). In this embodiment, unlike the offset fin, thecooling fin can be formed singly in a wave shape without needing splitblocks. As compared with the offset fin, the present embodiment canprovide a simpler manufacturing process with less number of componentsand process steps. Consequently, the cooling fin with reduced cost andimproved cooling efficiency and the manufacturing method of the coolingfin can be achieved.

The present invention is not limited to the above embodiment(s) and maybe embodied in other specific forms without departing from the essentialcharacteristics thereof. In the above embodiment, for instance, thecoolant flow paths 35 are formed by joining the cover plate 32 to thecooling fin 31. An alternative is to provide a casing 33 that houses thecooling fin 31 in which clearances (slits) between the fin parts areclosed by an inner surface of the casing 33 to form flow paths.

INDUSTRIAL APPLICABILITY

According to the present invention, the cooling fin with reduced costand improved cooling efficiency and the manufacturing method of thecooling fin can be achieved.

1. A cooling fin comprising a plurality of fin parts arranged in a rowand a base part integrally continuous to one ends of the fin parts tosupport the fin parts, wherein each fin part has a shape in which aproximal end portion continuous to the base part is straight and adistal end portion is wavy in a flow direction of a coolant which willflow through the fin parts.
 2. The cooling fin according to claim 1,wherein the distal end portion of each fin part has a wave shapedesigned to meet an expression (I):a≧f−w  (I) where “f” is a pitch of the fin parts, “w” is a thickness ofeach fin part, and “a” is a height of the wave shape of each fin part.3. The cooling fin according to claim 1, wherein the distal end portionof each fin part has a wavy shape including a region oblique withrespect to the coolant flow direction.
 4. A manufacturing method of acooling fin comprising a plurality of fin parts arranged in a row and abase part integrally continuous to one ends of the fin parts to supportthe fin parts, the method comprising the steps of: extruding a straightshaped fin including a plurality of fin parts each extending from thebase part into a comb teeth shape; and partially bending a distal endportion of each straight fin part in a direction intersecting anextruding direction to shape the distal end portion into a wave shape ina flow direction of a coolant which will flow through between the finparts.
 5. The manufacturing method of the cooling fin according to claim4, wherein the bending step includes arranging a jig in a clearancebetween the fin parts and bending the fin parts with the jig by coldworking.
 6. The manufacturing method of the cooling fin according toclaim 5, wherein the bending step includes placing the jig on one sideand the other side of each fin part in a staggered pattern, and applyinga load on the fin part by at least the jig placed on one side.
 7. Themanufacturing method of the cooling fin according to claim 4, wherein hebending step includes placing the jig in a position corresponding toclearances between the fin parts having just been extruded, and bendingthe fin parts with the jig by hot working.
 8. The manufacturing methodof the cooling fin according to claim 7, wherein the jig has comb teethinsertable in the clearances between the fin parts, and the bending stepfurther comprises moving the jig in the direction intersecting theextruding direction.
 9. The manufacturing method of the cooling finaccording to claim 4, wherein the bending step further comprises formingthe distal end portion of each fin part into the wavy shape including aregion oblique with respect to the coolant flow direction.
 10. Thecooling fin according to claim 2, wherein the distal end portion of eachfin part has a wavy shape including a region oblique with respect to thecoolant flow direction.
 11. The manufacturing method of the cooling finaccording to claim 5, wherein the bending step further comprises formingthe distal end portion of each fin part into the wavy shape including aregion oblique with respect to the coolant flow direction.
 12. Themanufacturing method of the cooling fin according to claim 6, whereinthe bending step further comprises forming the distal end portion ofeach fin part into the wavy shape including a region oblique withrespect to the coolant flow direction.
 13. The manufacturing method ofthe cooling fin according to claim 7, wherein the bending step furthercomprises forming the distal end portion of each fin part into the wavyshape including a region oblique with respect to the coolant flowdirection.
 14. The manufacturing method of the cooling fin according toclaim 8, wherein the bending step further comprises forming the distalend portion of each fin part into the wavy shape including a regionoblique with respect to the coolant flow direction.